One example of conventional batteries is a battery disclosed in Patent Document 1. A battery shown in FIG. 2 of this document has a flattened overall shape configured such that a “sealing plate 31” is fit in an opening of an “outer casing 10” opening at its one end. In the outer casing 10, a “spiral electrode body 20” is contained. In this battery, boundary portions of an open end face of the outer casing 10 and the sealing plate 31 are welded, thereby fixing the sealing plate 31 to the outer casing 10. This welding is made by irradiation of a “laser beam 50” from above to such areas to be welded (welding areas).